The subject matter of the present invention pertains to wellbore apparatus, and more particularly, to an apparatus interconnected between a pipe string and an object stuck in a wellbore and responsive to a pair of oppositely directed forces applied to opposite ends of said apparatus for releasing the pipe string from the object in response to a controlled application of the pair of oppositely directed forces to the apparatus.
When downhole tools, particularly a packer or perforating gun, are suspended from a pipe string in a wellbore, the tools may occasionally become stuck in the wellbore. When this happens, it may become necessary or desirable to disconnect the pipe string from the stuck tools. Devices designed to disconnect the pipe string from the stuck tools do exist in the prior art. Such devices include left hand thread safety connectors, simple tension shear out safety joints, wireline armed shear out safety joints, and wireline actuated pipe string releases. However, several disadvantages are associated with such prior art devices.
For example, tension actuated devices, having no protection against transient loads, must have their shear out level set higher than any expected transient shock loads, even though the duration of such transient shock loads is very short. Consequently, when an intentional actuation of the device is desired, a pulling force applied to the device, which is required to disconnect the pipe string from a stuck object in the wellbore, may be higher than a maximum threshold pulling force that a rig is capable of safely applying to the device.
Rotational devices, ones that require a left hand rotation of the pipe string to disconnect the pipe string from the device and release the pipe string from the device stuck downhole, are not susceptible to transient loads; however, such devices are susceptible to accidental actuation when an unrelated left hand rotation is applied to the pipe string. In addition, when the pipe string is disposed in a deviated well and it is necessary to disconnect the pipe string from an object stuck downhole, it is difficult to transmit the required torque to one end of the pipe string in order to rotate the pipe string and disconnect the pipe string from the device.
Wireline operated devices, ones which disconnect a pipe string from an object stuck downhole when a wireline is connected to the device and a required pulling force is applied to the wireline, require a clear path through the pipe string in order to connect the wireline to the device. Such devices are not suitable in cases where no clear path exists through the pipe string. For example, no clear path exists in a gun string or when there are items blocking the path in the pipe string, such as a drill stem test valve. This is especially true when sanding causes the object to be stuck downhole.